1. The Field of the Invention
The present invention relates generally to optical communication. More particularly, the present invention relates to modules for dynamically adding or dropping portions of an optical signal.
2. The Relevant Technology
Networks increasingly employ fiber optic technology to transmit information reliably via a communications network. Networks that employ fiber optic technology are known as optical communications networks, and are marked by high bandwidth and reliable, high-speed data transmission.
Optical communications networks often employ a technique known as wavelength division multiplexing (WDM) in order to maximize the amount of information that can be transmitted via the network. To employ this technology, a plurality of optical transmitters, located at the transmission nodes of the optical network, transmit optical signals. Each optical transmitter receives an electrical signal from a network device, such as a computer, and modulates the electrical signal via a laser to an optical signal having a distinct wavelength, called a channel. The distinct channels from the optical transmitters are then combined by a multiplexor to form a multiplexed optical signal. The multiplexed optical signal can then be transmitted via a single fiber optic cable to an optical network, such as a LAN backbone. A reception node of the network then receives the multiplexed, optical signal.
Once received by the reception node, the multiplexed optical signal is divided back into its constituent channels by a demultiplexor, and each channel is fed to one of a plurality of optical receivers for modulation into electrical signals. The electrical signals are then forwarded to a network device, such as a computer, for processing.
Not every channel, however, may be needed at a given time, and components on an optical network may need to communicate with each other through only one channel of a multiplexed optical signal. Alternatively, components simply may require fewer channels than are present in the multiplexed signal. As such, components may use add/drop modules to manage each of the different wavelength channels in an optical signal. As the name implies, add/drop modules are for adding or dropping component channels of an optical signal.
Add/drop modules are used frequently at nodes, or connection points, to manage exchanges of data channel signals in an optical network. Particularly, an add/drop module may drop an unused channel of a multiplexed signal while simultaneously adding a different, appropriate channel. Add/drop modules may interface directly with a computer to communicate Ethernet data from a fiber-optic network, in which case the add/drop modules are used to extract the channel of interest from the multiplexed optical signal. Add/drop modules also may be employed in transceivers or some other nodes in a fiber optic network.
More specifically, add/drop modules extract from the multiplexed signal those channels that are to be used by a device in the network. This enables components on a network, such as two computers, to communicate over the same wavelength, or channel, of a fiber optic signal, without necessarily interrupting bandwidth dedicated to the other channels in the signal. For similar reasons, the add/drop module also can be used to insert the dropped channel back into the optical signal, or to include different data that is encoded on the same wavelength as the dropped channel. One problem with conventional add/drop modules, however, is that they tend to be fixed, operating only on specific channels or wavelengths, and they generally cannot add or drop other channels without being replaced by a different add/drop module corresponding to the newly desired channels.
In addition to add/drop modules, optical networks also may employ various types of optical switches for switching and routing optical signals. One type of optical switch includes a matrix of thermo-optic switching elements interconnected by waveguides formed on a silica substrate. Other types of switches, known as planar optical switches, are available for some applications. Planar switches, such as switched directional couplers, represent an example of LiNbO3-based switches. In addition to traditional signal switching and routing, optical switching applications also may require selective optical signal filtering.
Although fixed wavelength add/drop devices are known in the art, there exists a need for add/drop devices that are configurable for use with a variety of wavelengths. Accordingly, a need exists for an optical add/drop module capable of wide-band WDM optical signal transmission and filtration. The optical add/drop module should be capable of dropping and adding a variety of channels without having to be physically replaced.